Method of treating filamentary tows



United States Patent 3,176,374 METHOD OF TREATING FILAMENTARY TQWS Arthur Murray Gardiner Kinnear and Thomas Henry Bull, Harrogate, England, assignors to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain No Drawing. Filed Apr. 2 9, 1963, Ser. No. 276,204- Claims priority, application Great Britain, May 7, 1962, 17,421/ 62, 17,422/62 14 Claims. (Cl. 28--72) This invention relates to filamentary tows made from synthetic linear polymers comprising polyesters based on terephthalic acid and those containing a major proportion of stereo-regular polypropylene.

During manufacture such tows are subjected to a uniform drawing process to bring about molecular orientation and crystallisation of the filaments. Such uniform tows are then converted into spun yarns, either by cutting the filaments into appropriate staple lengths followed by spinning, or by using a stretch-breaking technique on suitable tow to top converters followed by spinning. The staple fibres so produced have uniform shrinkage characteristics. It is known to submit filaments alternately to stretching and relaxing in a cyclic manner in a drawing zone, to yield filaments of improved but uniform properties.

We have found that spun yarns containing the synthetic staple fibres which have variable shrinkage characteristics, that is to say in which the individual fibres have different shrinkage properties or in which the shrinkage properties of the individual filaments vary along their length, before conversion into yarns, can give unusual and desirable effects when the yarns, or fabrics containing such yarns aresubjectcd to a heat shrinking treatment. The variable shrinkage in the fibres imparts, e.g., greater bulk and desirable colouring effects on the dyed yarns or fabrics, provided that the shrinkage characteristics are controlled between defined limits.

We now provide a process for making tows having variable shrinkage characteristics and by subjecting undrawn filaments to a drawing process in which the drawing conditions are continuously varied between defined limits. These tows are suitable for conversion into staple fibres and spun yarns.

According to our invention we provide a process for the production of filamentary tows of synthetic linear polymers comprising polyesters and polypropylene, as defined, which have variable shrinkage characteristics along their length and which are suitable for conversion into staple fibres and spun yarns, comprising subjecting a substantially uniform tow of undrawn filaments to molecular orientation in a drawing process using drawing conditions one parameter of which selected from draw ratio and temperature, is continuously varied between defined limits at substantially uniform time intervals, so that at a given to'w speed the attained optical birefringence of the filaments becomes 15-200 and their shrinkage in boiling water for 10 minutes l0%-60%, the intervals corresponding to a tow length which is greater than five times the shortest fibre length into which the tow is to be converted but less than 100 m., using draw ratios between 2:1 and 5:1, in a liquid medium maintained at a low temperature of 10 C.l00 (3., followed by converting the tow into staple fibres, tops and yarns, care being taken that the temperature of the filaments, fibres, tops and yarns is not allowed to rise above 50 C. in order not to affect the shrinkage properties of the filaments and fibres beyond the specified limits of shrinkage characteristics, before a subsequent heat shrinking operation.

One method of carrying out the proces of our invention comprises periodically varying the draw ratio under substantially uniform cyclical intervals. This may be done by varying the speed of the tow between feed means and draw rolls. This may be brought about by varying the relative speed, preferably of the feed means, whilst maintaining the speed of the draw rolls and also the temperature of the liquid medium used in the drawing process, substantially constant.

If the speed of the draw rolls is kept constant the filamentary tow can be forwarded, or wound up at a constant speed, which is desirable as it facilitates the further processing or winding at a constant speed.

The relative speed of the feed means can be varied by varying the speed of the feed rolls, e.g., by continuously variable gear drives or by other means, known per se, and which are preferably automatically regulated at regular intervals. Alternatively the speed may be maintained constant but the path length between the feed and draw means can be varied by suitable means.

Alternatively the speed of the tow and draw ratio is maintained constant but the temperature of the liquid edium is continuously varied preferably at a temperature from about 20 C. below the second order transition temperature of the unoriented filaments up to a temperature which is below that at which flow drawing conditions occur, in the case of polyester filaments.

If the intervals at which the drawing conditions are changed, are less than five times the desired shortest fibre length, then the overall variability in shrinkage between fibres when blended and spun into yarns will become diminished to such an extent that desired effects are reduced to an unacceptable level.

If on the other hand the intervals are greater than m. it becomes difiicult to blend fibres in such a way that for a given cross-section of the spun yarn, fibres having the full range of variable shrinkage characteristics are to be found. It should be appreciated that our tows when converted into staple fibres will give a continuous range of shrinkage characteristics within the specified limits 10 to 60% and are therefore distinct from, e.g., staple fibres obtained by drawing two tows, each under different but uniform conditions, followed by blending of the staple fibres. In our process the spatial distribution of fibre in the spun yarn having different shrinkage characteristics is more uniform than that obtained in a process involving the blending of fibre having two distinct levels of shrinkage. As a result a yarn with a more uniform but bulky cross-section is obtained.

Tow draw speeds from 30 to 200 m. per minute are suitable using multifilament tows above 100,000 denier. Slow speeds are required for heavier tows but for lighter tows higher speeds up to 100 m./per min. may be achieved, under suitable heat transfer conditions. The tows may be passed through a pre-draw frame bath containing a lubricant before being subjected to the drawing process under variable drawing conditions. It will be appreciated that the filaments after melt spinning should not be heated to a temperature which would affect the shrinkage characteristics, appreciably. The drawn tows are then crimped and cut into staple fibres or converted to spun yarns by a stretch-breaking process. If a stuifer box crimper is used for crimping, the tow when left wet from the drawing process, will have'its liquid content desirably reduced to below 10% based on the weight of the filaments. This tow may be left to dry in air, by passage over heated plates or by applying an air stream provided that care is taken that the temperature of the filaments is not allowed to rise above 50 C. Similarly during subsequent processing the temperatures should not be allowed to rise above 50 C. until the actual shrinkage treatment is carried out, usually this is done after the yarns have been Woven or knitted into fabrics.

which cause undesirable dye-flecks.

Using our drawing process, and a suitable liquid, such a as water, or an aqueous solution, emulsion or dispersion of a suitable surface activeagent, a wide range of draw ratios may be employed without resulting in excessive undrawn yarn. lfdesired, the tQW'rnay be split and combined with a longitudinal displacement, or with anothertow of'ditferent shrinkage characteristics so'thaton cut-,

ting, staple fibres having a continuously variable distribu I 'tion of shrinkage is obtained, out of phase.

It will be appreciated that the collection of the staple fibre from one process should take place'at'intervals;

which are greater than one wavelength in the shrinkage characteristics of the tow. I a In the case of tows made from polyethylene terephthalate filaments their birefringence in their undrawn condition should be at a substantially constant value between and 12x10" and that of the drawn tow having the variable shrinkage characteristics, a birefringence'varying continually along the length in the range of 30- 200 10-- units. Drawing temperatures below thesecond order transition temperature should be used .when varying the draw ratio.

. carding, gilling and drafting.

that a representative quantity of fibres within the range of shrinkage properties goes into a unit cross-section'of the spun yarn. Conveniently thisv may be achieved during The following examples illustrate but do not limit our invention. Examplesd to 4 relate to the process using variable draw ratios, and Examples 5 to 7 to the process using variable temperatures- Example l A'polyethylene terephthalate spun yarn tow of 8000 denier and ofbirefringence 267x10" was drawn between a pair of rollers whose ratio of peripheral speeds was caused to vary continuously between 3.58:1 and 4.5951 at a frequency of 1 cycle per minute, the peripheral speed of the drawing roll .being maintainedat 100 ft. per minute. The drawing zone, i.e., the yarn between the rolls, was maintained at60 C. by immersion in hot Alternatively if the variable shrinkage is to be obtained by continuously varying the temperature, this may be done by varying the. temperature of thefilaments between .50

and 100 C., at'intervals whilst maintaining the draw V ratio constant at a value above 2:1;

In the case of filaments made from'stereo-regular polypropylene tows iwith filaments having an undrawn birefringence of 3x10- which is raised to between 27x10" are suitable when varying the drawn ratio.

water. a Y The drawn yarn so'obtained with a birefringence varying between 145-185 X 10- had a boiling water shrinkage which varied-sinusoidally along its length at a frequency of 4.3' 10- cm.- with a maximum valueof 50% and a rninimum value of 25% in boiling water for 10 minutes.

, Example 2 V Yarn wasfprocessed as Example lbut drawn at 70 C.

The drawn yarn so obtained withthe same birefringence as in Example 1, had a shrinkage. which varied sinusoidally along its length at a frequency of 4.3 l0- cm.-

with'a maximum value of 30% and a minimum value of v V Example 3 V Yarn was processsed' as in Example 2 but the peripheral speed of the draw rolls was maintained at 50 f.p.m. The

' yarn so obtained with .the same birefringence as in Exused, but process control would have to ensure that the f two efifects are cumulative, i.e., in phase, or they may cancel each other out. a 7

In order to bring out the latent shrinkage characteristics of the fibres'the yarns or the fabric madefrom such yarn must be subjectedto a heat treatment. Temperatures of 90-160 C. are suitable in the case of I polyethylene terephthalate fibres.

Temperatures higher than V this mayinhibit the latent shrinkage properties because of premature'onset of crystallisation.

During the subsequent heat treatment which is desired to'cause shrinkage, two opposing phenomena occur: One brings about disorientation and the other crystallisation. If the rate of crystallisation is such" that the disorientation is inhibited, then the potential retractionrin length does not take place. i g V Polyesers having melting temperatures which are different from those of polyethylene terephthalate, will require corresponding adjustments in the treatment temperature both during drawing and in' the subsequent heat treatment, to bring out the latent shrinkage in the yarn or fabric, made therefrom. Because of the different degree of.

orientation in the fibres, the variability of shrinkage in the ample 1 had a shrinkage which varied sinusoidally along 1ts length with a frequency of 7.7){10' cm." with a maximum value of 40% and a minimum value of 25%.

Example 4 A polypropylene towof 1475 denier and of birefrmgence 30x10 units was drawn between a pair of rollers whose ratio. of peripheral speeds was caused to vary continuously between 2.25:1 and 5.50:1 at a frequency of 1' cycle" per minute, the-peripheral speed of the drawing roll being maintained at 100 ft./min.-The

drawing zone, i.e., the yarn between the rolls was maintained at 20 C. by immersion in water.

I The drawn tow so obtained with a birefringence varymg between 15-27 l0" had a shrinkage which varied sinusoidally along its length' at a frequency of 43X 10- CHIP-1 with a maximum value of 2 8% and a minimum valueof 10%, in boiling water for 10 minutes.

Exan'tpl 5- V A polyethylene terephthalate spun yarn tow of 8000 denier and of birefringence 2.67-was drawn,,in a Water fibres when blended, as happens in a spun yarn andfab- 1 ric, confer bulk, soft handle andcolour livelines s in thecase of dyed materials. v

Outside the specified limits and conditions of drawing insufficiently or undrawn, filaments and fibres are obtained should not be confused with the desirable controlled dye shade difference obtained in. our process. Also outside the specified limits, frequent filament breakage and stoppages occuryeventhough 'shrinkages within the specified limits of 10-60% may be achieved. A minimum spread 'of shrinkage characteristics of at least 25% is desirable.

During conversion of the tow into yarn care should be taken that sufiicient mixing of the staple fibre occurs so bath between a pair of partially immersed rollers whose ratio of peripheral speeds. was constant at 4:1, the penpheral speed of the drawing roll being maintained at m 200 f.p.m. The temperature of the water bath was caused to vary continuouslybetween 60 C. and C. at a frequency of 0.1 cycles per minute.

The; drawn yarn so obtained had a boiling water shrinkage which varied sinusoidally along its length at a frequency of .4 .0 10- cmrf with a maximum value of 45% and a minimum value of 13%.

Example Yarn wasp rocessed as in Example 1 but the draw ratio 7 maintained constant at 3.5 :1 and the bath temperature caused tozvary continuously between 60 C. and 70 C. at a frequency'of ()1 cycle per minute.

The drawn yarn so obtained had a boiling water shrinkage which varied sinusoidally along its length at a frequency of 4.0 10 cm.- with a maximum value of 58% and a minimum value of 34%.

What we claim is:

1. A process for the production of filamentary tows of synthetic linear polymer selected from the group consisting of polyesters based on terephthalic acid and stereoregular polypropylene, which have variable shrinkage characteristics along their length and which are suitable for conversion into staple fibres and spun yarns, comprising subjecting a substantially uniform tow of undrawn filaments with a birefringence of 12 10- to molecular orientation in a drawing process using drawing conditions one parameter of which selected from draw ratio and temperature, is continuously varied between defined limits at substantially uniform time intervals, so that at a given tow speed the attained optical birefringence of the filaments becomes 15-200 10- and their shrinkage in boiling water for 10 minutes 10%- 60%, the intervals corresponding to a tow length which is greater than five times the shortest fibre length into which the tow is to be converted but less than 100 m., using draw ratios between 2:1 and 5: 1, in a liquid medium maintained at a temperature of C.100 C., followed by converting the tow into staple fibres, tops and yarns, care being taken that the temperature of the filaments, fibres, tops and yarns is not allowed to rise above 50 C. in order not to affect the shrinkage properties of the filaments and fibres beyond the specified limits of shrinkage characteristics, before a subsequent heat shrinking operation.

2. A process according to claim 1 comprising periodically varying the draw ratio under substantially uniform cyclical intervals.

3. A process according to claim 1 comprising periodically varying the draw ratio by varying the speed of the tow between feed means and draw rolls.

4. A process according to claim 1 comprising varying the relative speed of the feed means whilst maintaining the speed of the draw rolls and also the temperature of the liquid medium used in the drawing process constant, and forwarding the tow at a constant speed.

5. A process according to claim 1 comprising periodically varying the draw ratio by continuously variable gear drives, which are automatically regulated at regular intervals.

6. A process according to claim 2 comprising periodically varying the draw ratio under substantially uniform cyclical intervals by maintaniing the speed constant while varying the path length between the feed and draw means by suitable means.

7. A process according in claim 1 in which the filamentary tow is made from apolyester based on terephthalic acid and the tow speed and draw ratio are maintained constant, while continuously varying the temperature of the liquid medium used for drawing the tow at a temperature from about 20 C. below the second order transition temperature of the unoriented filaments up to a temperature which is below that at which flow drawing conditions occur.

8. Aprocess in which the tow is passed through a pre-draw frame bath before being subjected to the process of claim 1.

9. A process according to claim 1 which includes crimping the tow after it has been drawn in said liquid medium, to remove excess liquid picked up during the drawing operation and reduce the liquid content thereof to below 10%, based on the weight of the filaments and then drying said tow by means selected from the group consisting of drying in air, passage over heated plates and air streams, care being taken that the temperature of the filaments is not allowed to rise above 50 C.

10. A process according to claim 1 in which the liquid medium is selected from the group consisting of: water, an aqueous solution of a suitable surface active agent and an aqueous dispersion of a suitable surface active agent.

11. A process according to claim 1 which the tow is split and combined with another tow of different shrinkage characteristics so that on cutting staple fibers having continuously variable distribution of shrinkage characteristics are obtained.

12. A process according to claim 1 in which the tows are made from polyethylene terephthalate filaments having the variable shrinkage characteristics and a birefringence varying continually along the length in the range of 30-200x10 using temperatures during drawing below the second order transition temperature.

13. A process according to claim 1 in which the shrinkage characteristics are brought out by a heat treatment at temperatures of -160 C.

14. A process according to claim 1 which includes splitting said tow into longitudinal portions, displacing said portions longitudinal with respect to each other and combining the thus longitudinally displaced portions so as to provide a draw variation across said tow.

References Cited by the Examiner UNITED STATES PATENTS 2,264,415 12/41 Taylor et al. 28-72 2,369,395 2/ 45 Heymann 28-72 2,541,181 2/51 Welton 161-173 2,894,802 7/59 Braunlich 28-72 2,917,805 12/59 Rokosz 28-72 2,917,806 12/59 Spence et al. 28-72 2,931,091 4/60 Breen 161-173 2,975,474 3 /61 Smith.

3,019,507 2/62 Maragliano et a1 28-72 DONALD W. PARKER, Primary Examiner. 

1. A PROCESS FOR THE PRODUCTION OF FILAMENTARY TOWS OF SYNTHETIC LINEAR POLYMER SELECTED FROM THE GROUP CONSISTING OF POLYESTERS BASED ON TEREPHTHALIC ACID AND STEREOREGULAR POLYPROPYLENE, WHICH HAVE VARIABLE SHRINKAGE CHARACTERISTICS ALONG THEIR LENGTH AND WHICH ARE SUITABLE FOR CONVERSION INTO STAPLES FIBERS AND SPUN YARNS, COMPRISING SUBJECTING A SUBSTANTIALLY UNIFORM TOW OF UNDRAWN FILAMENTS WITH A BIREFRINGENCE OF 0-12X10-3, TO MOLECULAR ORIENTATION IN A DRAWING PROCESS USING DRAWING CONDITIONS ONE PARAMETER OF WHICH SELECTED FROM DRAW RATIO AND TEMPERATURE, IS CONTINUOUSLY VARIED BETWEEN DEFINED LIMITS AT SUBSTANTIALLY UNIFORM TIME INTERVALS, SO THAT AT A GIVEN TWO SPEED THE ATTAINED OPTICAL BIREFRINGENCE OF THE FILAMENTS BECOMES 15-200X10-3 AND THEIR SHRINKAGE IN BOILING WATER FOR 10 MINUTES 10%60%, THE INTERVALS CORRESPONDING TO A TOW LENGTH WHICH IS GREATER THAN FIVE TIMES THE SHORTEST FIBRE LENGTH INTO WHICH THE TOW IS TO BE CONVERTED BUT LESS THAN 100 M., USING DRAW RATIOS BETWEEN 2:1 AND 5:1, IN A LIQUID MEDIUM MAINTAINED AT A TEMPERATURE OF 10* C. -100* C., FOLLOWED BY CONVERTING THE TOW INTO STAPLE FIBRES, TOPS AND YARNS, CARE BEING TAKEN THAT THE TEMPERATURE OF THE FILAMENTS, FIBRES, TOPS AND YARNS IS NOT ALLOWED TO RISE ABOVE 50* C. IN ORDER NOT TO EFFECT THE SHRINKAGE PROPERTIES OF THE FILAMENTS AND FIBRES BEYOND THE SPECIFIED LIMITS OF SHRINKAGE CHARACTERISTICS, BEFORE A SUBSEQUENT HEAT SHRINKING OPERATION. 